Two-stage Rocket Climbs To 15 Km, Promptly Gets Lost

Last month, the Cambridge University Spaceflight society launched two stages of their Martlet 1 three-stage rocket. After seeing our call for rocket builds, they sent in a launch report. We’re glad they did; it’s an amazing piece of work that screams into the atmosphere faster than the speed of sound.

The society is designed the three-stage Martlet 1 with the goal of reaching 15km (50,000 feet) over a launch range at Ben Armine in Scotland. This launch was a test of stage separation, intended to work out any bugs in the system before going to the full-sized rocket.

When Martlet 1 takes off, it’s 1st stage engine fires for 5 seconds and coasts for another 9 seconds. In the video after the break, the guys expected to hear the pop of the second stage igniting after 14 seconds. The team forgot to account for the fact the rocket would be 3km in the air at that time, and thanks to the slowness of sound the second stage was heard though the clouds at 25 seconds after launch.

With rockets, hardly anything goes exactly as planned, so unfortunately the team only recovered the bottom half of their rocket. After searching over 60 square km for the second stage, the guys realized it might be lost to the moors of Scotland. Hopefully the second stage will turn up soon so the full 3 stage stack can be realized.

With rockets, hardly anything goes exactly as planned, so unfortunately the team only recovered the second stage of the rocket. After searching over 60 square km for the second stage, the guys realized their rocket might be lost to the moors of Scotland. Hopefully the second stage will turn up soon so the full 3 stage stack can be realized.

Wow… you don’t get a good sense of scale from the videos. But from the photographs on their web site it looks like each stage is a bit taller than a person, and the body of the rocket is about the diameter of a person’s arm.

We then began to franticly track the rocket stages as they flew through the air. Both stages were equipped with GPS trackers that downlink via radio on the 434MHz band. Tracking was a nightmare however, as the frequency we received had a huge Doppler shift due to the speed of the rocket. Because the rocket had disappeared through the clouds, it was also extremely difficult to keep the directional antenna pointing in the direction of the rocket, and we soon lost it as it disappeared over the visible horizon.
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Without a decent tracking direction for the second stage, we had to make some educated guesses as to the likely flight path. We spent the last two days of the launch campaign trekking over 40km through the launch range, through bright sunshine and through horizontal rain, sleet and snow. Despite searching over 60 square kilometres of the range, the second stage is still missing in action (presumed awesome). We just hope the gamekeeper finds it soon……

Maybe a good amateur radio band transmitter would work better and still be able to transmit a beacon over a long distance after splashdown.

APRS – Even though many of us who built this rocket have a full amateur license, you’re not allowed to use it airborne. This limits you to license exempt frequencies set asside for things like garage door remotes. In our case, we only had 10mW on 434MHz to implement our link, and 10mW is very little so we can’t do things like 1.2kBaud APRS (we used 50 baud rtty).

Android – we were miles from anywhere with phone signal. It really was a very remote part of the Scottish highlands. We had a sat phone to call the aviation authority – that was it.

Being a ham but not having looked into APRS much, I was unaware of the limitations.
Still, it could possibly be useful in locating rocket sections if there was a way to activate it after they had returned to Earth.
Maybe it would get to be too complex/heavy by then.

Not sure how your amateur radio is over there, but we over here in the US have quite a good selection we can run telemetry on. As long as you ID, and you’re not trying to obscure the meaning of the transmission, it’s OK.

So how does this stuff scale up? All space rockets are huge because at the time they were developed a device that would make minimal practical sense would weigh like 100kg (a) and the primary cause for rocket development has always been delivering nice explosive payload (b). Now that we can have extremely tiny satellites without explosives: can a tiny Arduino-satellite be launched by a tiny rocket?

Not much space for optics, nor large radio antennas, nor science experiments… unless they involve dustmites. It’s nice that you can cram the basic components of a satellite in a matchbox, but all the useful stuff is bigger and heavier than that.

Many of the rockets are so large in diameter because they use liquid fuel rather than solid fuel that the vast majority of amateurs use. As you said, the first and second geneartion space vehicles were ICBMs without a warhead. The reasoning behind using liquid fuel for those is mainly one of storage stability. Few people like to have tons and tons of fuel and oxidizer combined just sitting around. It does age and break down over time. So after decades of sitting in a silo pointed at Russia/the United States some team of poor saps would have to essentially rebuild it. With liquid fuel, they would fill it up minutes before launch.
Additionally liquid fueld rockets allow one to throttle the thrust, and somewhat more importantly abort a launch. If something happens in the seconds after main engine ignition on the now retired shuttle they could still abort the launch. Once the solid fuel boosters(the two side rockets) kick off, the shuttle -is- leaving the launch pad in a generally upward direction.

Furthermore peaceful space faring rockets are so huge because it costs billions of dollars per pound of payload. So you want to make your launches count.

Sounding rockets scale up ok, but sounding rockets just go up and come strait down again. To get into orbit, you must carry hundreds of thousands of pounds of fuel up to about 80km, then turn sideways and accelerate to about 7 or 8 km/s. Every extra pound you want to lift to orbit requires hundreds of pounds of fuel. That is why the rockets are so big.

Unfortunately you can’t scale down orbital rockets. As you decrease the diameter and height, the volume of fuel goes down faster than the weight of the fuel container. The SpaceX Falcon 1 rocket is close to the smallest thing that can get a payload to orbit at 21m tall and 1.7m wide.

Of course this all changes if you don’t use a classical rocket. If you strap a smaller rocket to a jet and fly it up as high and as fast as you can before igniting it, you can make them a bit smaller. This is how the Orbital Science Segasus works. It is a bit smaller at 16m tall and 1.2m wide.

Well, I guess this is the Cambridge Lads’ “Here, hold my Guiness” school of flight planning.

A note to all would-be rocket scientists – if you’re going to turn your back and shoot your rockets into the clouds (maybe not much choice over the land o’ Haggis) and let them fall where they may, you might wish to add an actual beacon.

A beacon is very low tech, but will let you find your errant rocket stage with little effort. A proper beacon uses low frequency and can be picked up with a proper directional antenna with little effort. It can be found around corners, even if the rocket has embedded itself into the corpse of Warren Zevon, or the bog.

They are simple to build, and cheap insurance.
Even if it only chirps once per minute (days of beacon action) or once every 3 seconds, you’ll find it pays big dividends.

PS2 – Seriously, estimated cloud bases are available by telephone from, oh, anywhere on the planet where engish is spoken with a functioning aviation ministry/department.

dear svofski – orbit is well beyond the grasp of these guys… While they have wonderful and amazing high-tech resources that were unavailable 50 years ago, they still have to solve the exact same set of problems the guys with german accents and slide-rules did.

All space programs are the same, including big ones like that of China – until they manage to relearn the basics – lessons about design, materials, manufacture, math and procedures (which are available for free from historical documents that nobody can be bothered to dig through because they are obscure and boring), they have to make all the same mistakes everyone made 5 decades ago.

There is nothing whatsoever wrong about doing this, and I am impressed by the project… but the ability to lob a webcam into orbit is a long, long, looooong ways away from where these guys are.

Fins don’t work that well when there’s an atmosphere, and they’re next to useless above 85,000 feet. And that’s just standing on the curb in front of space’s sidewalk.

I dropped rocketry for pneumatic cannons when I could not scale up without a license of my own.

So how about combining the two? It is rather trivial to get something up to 120 meters per second with a five minute stop at the hardware store. That could save a significant amount of fuel to break the initial inertia.

This is something I wonder about. Having never had an original idea in my life, I wonder why nobody has ever sent up a rocket with a balloon first, and then launched from that 85000 to 100000 foot to make that trip – or perhaps as you suggest, something to “kick off” the rocket.

Some shoulder-launched missiles, for example, use a charge to get out of the tube, then the motor engages, but on a smaller scale.

The idea of going with fuel from launch pad to space came about in the early years, before the availability of the kinds of materials and processing power that we have today. I don’t have the skills for this, but certainly the guys who already dabble in this might have gotten the idea. Must be easier said than done, like many things.

A pneumatic cannon to launch an amateur rocket sounds like a good idea (giant styrofoam sabot anyone?) put an accelerometer in it to fire its own engine once acceleration begins to slow and you could probably get some really impressive height.

He’s right – say kids, get anything knit – from an old tube sock or scarf to cheesecloth to a really old t-shirt. Even pantyhose. Cut a square out, and fold it up. Don’t forget the breath test – it has to be loosely woven enough to breath through easily. If you have to work at it, it’s too tight.

use a Rubber band to clip it over your microphone – and you are using an external mike, right? Built in mics suck.

Voila! You can hear… sounds. You can accomplish the same thing by sticking the external mike in a tin can large enough that the wind is baffled, but not so large that the wind strikes the mic.

It needs to be large enough that air moving over the can won’t vibrate the can, ala the musical pop bottle effect. You can also use yarn, but it’s a lot of work.

athletic sock – something puffy and thick, and then put it on your fist and fold it so you have about 3 layers of sock